How to Prune Your Email List to Improve Deliverability

by Today's Eggspert

Last updated on July 20th, 2017

As with all marketing channels, email marketing is only effective if it reaches its desired audience. For email, that means reaching the inbox.

But 21% of opt-in emails fail to reach the inbox. Deliverability and reputation are crucial to reaching the inbox. A major component of reputation is keeping a clean list.

List hygiene can be considered a “pruning” process. And just as one prunes a tree to make it stronger, you should prune your email list to ensure good deliverability. Let’s look at how to do that.

1. Cut the Dead Weight

Remove Duplicates

Depending on what platform you’re using to send your email, duplicate email addresses can create issues—namely, some of your subscribers can receive the same email multiple times. These duplicates can create customer disconnect and cost you both time and money.

De-duping your list is a must. Fortunately, most email service providers will de-dupe your list for you upon uploading it into their system. That’s because they use the email address as the “unique identifier” for records in their system, and they’ll update information attached to email addresses, but not allow said email addresses to be in the lists more than once.

If your system doesn’t do that for you, or you have multiple, different email addresses for individuals, you’ll want to do some manual list management and de-duping yourself. You can do it manually (hello Excel or Google Sheets!) or have an email list verifier tool (like BriteVerify, Kickbox, or FreshAddress) do it for you.

In Excel, in its simplest form, you can:

  1. Select/highlight your column or row (most likely a column)
  2. Click on the Data tab
  3. Then click on Remove Duplicates and follow instructions

ACROBAT Data Remove Duplicates

In Google Sheets, according to

  1. Select the cell where you would like the de-duplicated info to begin
  2. Enter the function =UNIQUE(
  3. Select the cells you would like to pull data from
  4. Close the parentheses. Your function should look something like: =UNIQUE(B:B)

NOTE: Most ESPs require that you upload your list saved as a .CSV file (or comma delimited).

Remove Bad Email Addresses

Bad email addresses increase your bounce rates and negatively impact your sender reputation. Regularly removing these hard bounces and unknown users is one way to help ensure great deliverability.

Here are ways you can combat bad email addresses further:

  • Never purchase email lists. Purchased lists are typically chock full of invalid and other bad email addresses. (In the US, this is technically not illegal. In many other countries, it is illegal.)
  • Employ double opt-in / confirmed opt-in procedures. Requiring subscribers to confirm their email addresses can help ensure bad email addresses don’t end up on your list in the first place.
  • Ask subscribers to update their contact information. Periodically, send an email to subscribers asking if they still want to hear from you. Bonus: You can use this opportunity to gather additional subscriber information for segmentation purposes later.

2. Separate Actives and Inactives

If you continually mail your entire list, subscribers who never engage can bring down your reputation and affect delivery to your most active customers. Therefore, separating your active subscribers from your inactive subscribers is an important step toward protecting yourself from reputation harm.

To start this separation:

Define “Active” and “Inactive” Users

Generally, your “active” subscribers are those who demonstrate continual engagement with the emails you send—they open, they click, they even convert. In terms of “inactive” subscribers, the definition can change dramatically depending on the industry you’re catering to.

An obvious “inactive” may be a subscriber who joined the list two years ago and has never opened or clicked on an email you’ve sent. When you get more granular than that, it’s a bit tougher to define.

For example, if you’re a daily deals site, you may define an “inactive” user as someone who hasn’t engaged with your emails (or engaged with your website) in 30 days. If you’re a traditional retailer, maybe you push the time frame out to 90 days. And if you’re selling a once-a-year purchase, maybe your time frame is even longer than that.

However you wish to define inactivity among your subscribers, it’s important to not just consider email engagement, but also engagement with your website as a whole. Perhaps email engagement is zero, but those subscribers are still purchasing from you. Would you stop email? Not necessarily.

For example: Perhaps you get zero engagement with an email whose subject line is “Your bill payment is due.” If the bills are getting paid, is that email unsuccessful? Maybe not.

Find the definition that makes the most sense for your brand, your industry, and your product lifecycle—and be sure to test different definitions over time as well.

Segment Actives from Inactives

One term for this is “engagement-based filtering.” Essentially, create two lists or segments (depending on how your ESP works),  one for active subscribers and the other for those you deem inactive.

3. Let “Sleeping Dogs” Lie… Temporarily

Remove inactives from your normal mailing schedule—let them “sleep.” Continually mailing this group only drags your reputation down. So, give them a break from your regular emails and drop them into a special winback/re-engagement program (below).

Trigger a Winback/Re-engagement Program

For inactives to re-engage, clearly you need to do something different. (What’s that thing about the definition of insanity?) A special, automated email campaign specifically targeting inactives could be the ticket to re-engaging these dormant subscribers.

You can try:

  • Special incentives (that they wouldn’t see in your normal campaigns) that are specifically designed to garner action out of these subscribers
  • A special service message asking for more information, how you can do things differently, etc.
  • A direct request for activity or an unsubscribe (perhaps with an assumption of an unsubscribe as well)

Whatever you try, it needs to be different content than what they’ve been seeing—and ignoring—for months on end.

Carters Reengagement

The Body Shop Reengagement

4. Prevent Inactivity with Relevant Content and Proper Frequency

File this under “Easier said than done.” Relevant content with attractive offers that are sent continually at the “right” times is the best way to prevent inactivity and list churn.

To ensure your content is relevant, match your messaging to what you promised at opt-in. Sync up this content with known subscriber preferences and data, and make sure your email copy and CTA are in perfect harmony with your subject line and preheader text. Finally, make you’re your emails look good on all devices (mobile, tablets, and desktops). No matter how good or “relevant” your content is, if it looks bad, folks will dismiss it.

Email frequency is another major factor in preventing inactivity, yet is incredibly difficult to gauge. Why? Because what’s “too much” for one subscriber may be the perfect amount for another. Use your segments and test different cadences. Odds are, your most engaged subscribers will be fine with receiving more emails while your inactive group would prefer to see fewer emails from you in their inbox.

Unfortunately, in both cases, you’ll just have to learn what works best for your subscribers. There’s no “silver bullet” frequency or content. There’s no “best time” to send. Every brand and every mailing list are different.

5. Decide What to Do with Your Truly Inactive Subscribers

In the email marketing industry, this is a major point of contention. Some will argue that once a subscriber is inactive, they should be deleted from your list. Others will argue that every subscriber is sacred and should never be removed until they specifically tell you to remove them (with an unsubscribe, a spam complaint, and an email laced with 4-letter words…).

Here’s what you can do:

  • Do not delete, but monitor how your inactive segment performs.
  • Reintroduce the inactives back in to your regular mailing schedule and see if any wake up on their own.
  • Delete the subscriber.

If you think your deliverability is suffering, lean toward any path of action that removes potential harm. So, if you think your deliverability is bad, delete inactives. If your delivery is strong, perhaps you can hold on to them a little bit longer.

Switching ESPs Doesn’t Solve All Delivery Problems

If you’re having delivery issues on your email service provider, switching ESPs for that sole reason may not fix your problem. If you’re going to keep your same, potentially bad practices, you’ll find very quickly that your delivery tanks on your new provider.

That said, if you are planning to switch to a new ESP, plan the move well in advance. You’ll need to move over your unsubscribe list and make sure your lists are clean and up to date. Your IP address reputation may not follow you, but your domain reputation will.

Another word of advice here: Start sending on your new ESP’s IP address only with your active subscriber list. Their engagement will build up your reputation, perhaps even to the point where you can open the flood gates up a bit more. But, patience is key.

NOTE: Good ESPs will remove bad email addresses from your list (aka hard bounces) after your first mailing. Others will allow you to set rules in terms of how to handle “soft” bounces and other list issues. However, if your list is full of bad email addresses and a host of other issues, your account will likely be flagged by your ESP and you’ll be put into their “penalty box” for a while, or even kicked off altogether.

What Does Your Current Email Service Provider Do For You?


  • How AWeber handles undeliverables: AWeber will continue to send messages to a subscriber that returns an undeliverable message (hard bounce) three times. After the third undeliverable response, they will automatically unsubscribe those email addresses.
  • AWeber will close down abusive accounts (this helps everyone using AWeber for email marketing).
  • AWeber has a Director of Deliverability who maintains relationships with the large email providers. This high-level line of communication helps to ensure compliance with all the major email providers.

AWeber recommends going through your lists and looking for people who haven’t read an email in recent months. They suggest that you run a re-engagement campaign to those people. For the people who don’t respond, you should remove their email addresses and delete them from your AWeber account. These email addresses are taking up space on your account which costs you money.


  • Meet Omnivore – MailChimp has developed an internal technology that compares more than 61 trillion data points to predict abusive behavior before a campaign is ever sent. The idea is to prevent the “bad apples” that also use MailChimp from spoiling the fun for everyone.
  • All MailChimp users automatically get free authentication when they sign up for an account. Authentication is a really helpful method to make sure emails get accepted by large email providers.
  • MailChimp groups hundreds of IP addresses into different reputation levels. This way, they can nurture individual IP addresses to become better at deliverability over time.

Constant Contact

  • Like MailChimp, Constant Contact offers authentication for all accounts.
  • If a Constant Contact IP address is placed on a blacklist, their team quickly jumps on it to reassign accounts to “good” IP addresses or “de-list” them.
  • Constant Contact works with their competitors to forge industry best practices.

Here’s a detailed page of tips to fix bounces if you’re using Constant Contact.

Closing Thoughts

As cluttered and competitive as it may be, the inbox is still the goldmine for email marketers, and you can’t get there without having your delivery ducks in a row. A clean list is a requirement for good delivery. So spend the time to clean your list.

Then the subscribers who want to hear from you, will. And those who don’t, won’t. It may seem dull, but if you’re marked by spam filters and ISPs, you’ll wish you’d done it.

About the Author: Scott Cohen is the VP of Marketing at InboxArmy, full-service email marketing agency. He has been living and breathing email marketing since 2007. With both agency and client-side end-user experience, Scott brings a unique perspective to email marketing that combines best practices with real-world-tested strategy and tactics. Check out Scott’s email marketing tutorials and articles on Email Marketing Blog. He has recently published an eBook on “Your Email Creative” that discusses at length the rendering challenges and some actionable tips to overcome them. Download Now!

*Featured image source: Scissors by iconoci from the Noun Project

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